Such systems are known per se and are described in various publications. Primarily in the field of direct injection combustion engines that operate according to the compression ignition or the spark ignition methods, the demands on injection systems with respect to the allocated amount, the time and the rate-of-discharge curve are ever increasing. Rate-of-discharge curves have thus been modified over the last years such that either the injection amount to be allocated to a combustion cycle is split into a plurality of partial injections, or the rate development forming is controlled through a modulation of the fuel pressure or other rate-modulating measures. In order to be able to reproduce these rate-of-discharge curves in an exact manner, if possible in real time, corresponding systems must be provided with which the injection behavior of individual fuel injectors can be reproduced as exactly as possible.
DE 103 31 228 B3 describes a device for measuring time-resolved volumetric flow processes, in particular injection processes in internal combustion engines. This device includes a rotary displacement device arranged in a bypass line and a movable piston arranged in a measurement chamber, the piston having the same specific weight as the measuring liquid. The piston has a sensor associated thereto whose generated voltage is a measure of the piston travel when injections occur. The voltage generated is supplied to an evaluation unit that continuously detects the travel of the piston in the measurement chamber and graphically represents flow processes with high temporal resolution. Control electronics provide for a control of the rotary displacement device such that the rotational speed of the rotary displacement device remains constant during a working cycle of the injection system and substantially corresponds to the mean throughflow throughout the working cycle. This device allows for a representation of flow processes with high temporal resolution so that both total amounts and exact developments can be represented and evaluated.
This device is, however, disadvantageous in that longer thermal setting times exist because of the energy input by the injection into the measurement chamber. Up to the present, attempts have been made to compensate for the measuring inaccuracies resulting therefrom by compensation constants obtained by preliminary measurements. However, inaccuracies persist since these constants are not always exactly known.
DE 100 64 509 A1 describes a method for calibrating path sensors wherein, prior to the actual measurement, a calibration table is built from quadruples of temperature, pressure and measuring signal of the path sensor. In order to allow this table to be built, an annular space can be tempered, i.e., certain temperatures can be set in the annular space. This compensation can only be performed at a high expenditure of time for calibration purposes and must be repeated for each additional valve. In addition, a new setting process takes place in the system upon every injection so that, for an overall injection formed by a plurality of individual injections, an exact measurement cannot be represented with any resolution, since no individual temperature changes can be measured.